Moving coil instrument with stretched strip suspension



June 19, 1956 F. ENDLICH ETAL MOVING COIL INSTRUMENT WITH STRETCHEDSTRIP SUSPENSION Filed March 3, 1955 3d. 9 .9 H 3 ml 7 3. m m 42 a 5Fig. 7

United States Patent MOVING COIL INSTRUMENT WITH STRETCHED STRIPSUSPENSION Friedrich Endlich, Langen in Hessen, and Walter Hufbauer,Frankfurt am Main, Germany, assignors to Hartmann & Braun-Aktiengesellschaft, Frankfurt am Main, Germany, a corporation of GermanyApplication March 3, 1953, Serial No. 340,018 Claims priority,application Germany March 8, 1952 12 Claims. (Cl. 317-468) Thisinvention relates to an electrical measuring instrument employing amoving coil being suspended between two taunt strips, enclosing a coreand moving in a magnetic field. Such taut suspensions provide the stripsto be stretched by means of springs. These springs are also supposed toabsorb shocks elastically to which the instrument is exposed. Provisionsmust be made, however, that the movements of the coil due to the tautsuspension be limited, because otherwise a too high stress will occur inthe taut strips and thus result in a rupture. In the direction of theaxis of rotation the core represents a limit because the front side ofthe moving coil fits to the front side of the core. Such a limitvertically to the moving coil, however, does not exist in any case andmust specially be provided for in order to prevent the movements of thecoil to become too violent in this direction.

The invention specially relates to the arrangements of stops limitingthe movement of the coil in the vertical direction to its plane. Theinvention avoids to a high degree additional components for theconstruction of these stops and thus quite a simple design is possiblenecessitating no further space.

The invention provides guide parts at the moving coil which with someclearance protrude into recesses at the front side of the core. movementof the coil, the guide parts being fastened at the moving coil andvariable with regard to their position, so that the moving coil can bepushed over the core and the guide parts inserted in the recesses.

Another possibility would be to fasten tightly the guide parts at thecoil and to provide the core with additional recesses where the guideparts are able to pass through when pushing the moving coil over thecore. This done, the recesses can be closed if required.

Examples of the invention are shown by the relevant figures.

Figs. 1 and 2 show the invention with regard to a core magnet system, i.c. Fig. 1 shows a vertical sectional view and Fig. 2 the view fromabove.

Figs. 3 and 4 show another construction also as sectional view and fromabove.

Figs. 5 and 6 show a design where additional recesses are provided inthe core and where the guide parts are inserted.

In Figs. 1 and 2 the core is marked with 1 and around which the movingcoil 4 turns. The moving coil 4 suspended between two stretched strips 3which are tightened by the leaf springs 14. 9 stands for the pointer.The strips 14 are held by a support 15 fastened to the ex ternal ringshaped yoke 16 which are both fastened to the core 1. The example showsa so-called core magnet system where the internal core 1 is to be thepermanent magnet, that means of permanent-magnet material, and whereexternally a ring shaped yoke 16 consisting of soft iron is provided.

The invention, however, is likewise applicable for a system withexternal magnet, that means where core 1 These recesses limit thelateral consists of soft iron and where at the external side the polepieces of for instance a U-shaped permanent magnet generate the magneticfield.

There are two cylindrical recesses 2 provided at the front sides of thecore. When manufacturing the core for instance which is oftenaccomplished by means of moulding, these recesses can already be madeduring this stage of manufacturing. At the internal front sides of themoving coil two thin metal plates 5 and 5 of nonmagnetic material arefastened. The latter are stretched before mounting the system as shownby the upper plate 5. After having pushed the moving coil over the core,both free ends of this little plate are bent into the recess of the coreas illustrated below by 5'. They must be a size that these recesses arejust filled with some clearance. These guide parts are meant to be thestops for the movement of the coil. If the coil is moved in thedirection of the arrow, i. e. vertically to its plane, the bent downends of the guide parts hit upon the internal edge of the recess andthus limit the movement.

A second possibility is to use elastic material for the plates 5 and tobend down their ends already before mounting. When pushing the movingcoil over the core, these plates are bent back until the core can beslipped over easily and then engage without any help in the recesses 2of core 1. In this case both guide parts act simultaneously as anelastic stop for movements of the coil in the direction of the axis ofrotation.

Another design is illustrated by Figs. 3 and 4 where the fastening ofthe stretched strips and the external part of the magnetic circuit areomitted in order to simplify the illustration. Again the moving coil ismarked with 4 and the core with 1, the stretched strips with 3. Thepointer 9 is extended beyond its fastening at the moving coil andrepresents itself the guide part. For this purpose the pointer is bentdown at 8 and engages in a circular recess 7 in the core. The protrudingend of the pointer simultaneously carries the counterweight 10. If therecess in the core is provided for accordingly it can act simultaneouslyas stop for limiting the deflection.

Figs. 5 and 6 show another solution where the insertion of the guideparts is rendered possible by additional recesses in the core. The samesymbols are again chosen for core, support, stretched strips etc. as inFigs. 1 to 4. Again a cylindrical recess is provided in the core as inFigs. 1 and 2. In addition, however, there is recess 12 resembling anarrow slot. Through this slot the guide parts can be inserted which inthis case are fixed inelastically at the coil. If this slot should proveto be inconvenient it can be closed subsequently by some suitable part.The present case shows an example where it is not necessary to closethis slot. The guide parts are made of two springs 11 which in theirnormal condition are spread out like a fan. They are pressed togetherwhen the support is inserted and can thus be led through the guidingslot. They then spread out within the cylindrical part and act as stopsfor limiting lateral movements.

We claim:

1. A measuring instrument having a moving coil, a core, a pair of stripsand springs, the coil being fixed to the two strips stretched by thesprings, said coil turnable around the core, guide parts fixed to thecoil, a face of said core having a recess, the guide parts having endsprotruding into said recess, said recess being shaped so as to allow theprotruding ends of the guide parts to move in their orbits but havingonly a clearance in radial direction smaller than the least distance inradial direction occurring between the coil and any other part of theinstrument.

2. A measuring instrument as in claim 1, the material of said guideparts being of such kind as to allow deformation.

3. A measuring instrument as in claim 2 said material being elastic.

4. A measuring instrument having a moving coil, a core having an endface, the core having a recess in the zone of the end face, a pair ofstrips and springs, the moving coil being fixed to the tWo strips andstretched by the springs, said coil being turnable around the core,guide parts fixed to the coil, said guide parts consisting of sheetmetal strips the ends of which are bent, the bent ends of the sheetmetal strips being turnable in orbits about the axis on which the coilturns and protruding into the recess, said recess being shaped so as toallow the protruding ends of the guide parts to move in their orbitsfreely in an angular direction about said axis, but having walls near tosaid orbits and ends, the clearance between the ends and the walls in aradial direction being smaller than the least distance in radialdirection occurring between the coil and any other part of theinstrument.

5. A measuring instrument having a moving coil, a core, springs and apair of strips, the coil being fixed to the two strips stretched by thesprings, said coil being turnable around the core, guide parts fixed tothe coil and having ends movable in arcuate orbits as the coil isturned, an end face of said core having a recess, said ends protrudinginto the recess, the recess and walls thereof being shaped so as toallow the protruding ends of the guide parts to move in their orbits buthaving a radial clearance from the walls smaller than the least distancein radial direction occurring between the coil and any other part of theinstrument, said core having in addition a radial slot shaped so as toallow the guide parts to pass radially into the recess when the coil isslipped over the core.

6. In a moving coil instrument, a base; separated spring mounting prongson and projecting in a common direction from the base; a cylindricalcore of magnetic material between the prongs, and fast with respect tothe base, and provided at one end with a recess having arcuate wallscoaxial with the core and open toward one of the respective prongs; amovable coil around the core and each end thereof and adapted tooscillate about the axis of the core; a pair of strips each lyingsubstantially along the axis of the core and normally in a common plane,each strip having one end portion secured to one prong and the other tothe coil to provide a torsion suspension for the coil to oscillate aboutsaid axis; and a detent member secured in fixed relationship to the coiladjacent said one end of the core and projecting into the recess clearof the walls thereof and so near the walls that the detent memberprevents radial motion of the coil to a predetermined degree.

7. In a moving coil instrument, a base; separated spring mounting prongson and projecting in a common direction from the base; a cylindricalcore of magnetic material between the prongs, and fast with respect tothe base, and provided at each end with a cylindrical recess coaxialwith the core and open toward the respective prongs to provide aprojecting annular flange, a movable coil around the core and each endthereof and adapted to oscillate about the axis of the core; a pair ofstrips leach lying substantially along the axis of the core and normallyin a common plane, each strip having one end portion secured to oneprong and the other to the coil to provide a torsion suspension for thecoil to oscillate about said axis; and detent members secured fast tothe inner portion of the coil adjacent the end faces of the core andprojecting into the respective recesses clear of the inner walls of theflange and so near the walls that the detent members prevent radialmotion of the coil to a predetermined degree.

8. In a moving coil instrument, a base; separated spring mounting prongson and projecting in a common direction from the base; a cylindricalcore of magnetic material between the prongs, and fast with respect tothe base, and provided at one end with an arcuate recess having arcuatewalls coaxial with the core and open toward one of the respectiveprongs; a tubular flux conductor of magnetic material fixed on the baseand coaxial with and surrounding the core and spaced therefrom, amovable coil around the core and each end thereof and adapted tooscillate about the axis of the core in the annular space between theconductor and core; a pair of strips each lying substantially along theaxis of the core and normally in a common plane, each strip having oneend portion secured to one prong and the other to the coil to provide atorsion suspension of the coil to oscillate about said axis; and adetent member secured fast with respect to the coil adjacent the saidone end of the core and projecting into the recess clear of the wallsthereof and so near the walls that the detent member prevents radialmotion of the coil to a degree suflicient to prevent the coil fromcoming into contact with the core and conductor.

9. In a moving coil instrument, a base; separated spring mounting prongson and projecting in a common direction from the base; a cylindricalcore of magnetic material between the prongs, and fast with respect tothe base, and provided at each end with a cylindrical recess coaxialwith the core and open toward the respective prongs to provide aprojecting annular flange; a tubular flux conductor of magnetic materialon the base and coaxial with and around the core and spaced therefrom, amovable coil around the core and each end thereof and adapted tooscillate about the axis of the core in the annular space between theconductor and core; a pair of strips each lying substantially along theaxis of the core and normally in a common plane, each strip having oneend portion secured to one prong and the other to the coil to provide atorsion suspension for the coil to oscillate about said axis; and detentmembers secured fast to the inner portion of the coil adjacent the endfaces of the core and projecting into the respective recesses clear ofthe walls thereof and so near the walls that the detent members preventradial motion of the coil to a degree sufficient to prevent the coilfrom coming into contact with the core and conductor.

10. In a moving coil instrument, a base; separated spring mountingprongs on and projecting in a common direction from the base; acylindrical core of magnet material between the prongs, and fast withrespect to the base, and provided at one end with a cylindrical recesscoaxial with the core and open toward one of the respective prongs toprovide a projecting annular flange; a tubular flux conductor ofmagnetic material on the base and coaxial with and around the core andspaced therefrom, a movable coil around the core and each end thereofand adapted to oscillate about the axis of the core in the annular spacebetween the conductor and core; a pair of strips each lyingsubstantially along the axis of the core and normally in a common plane,each strip having one end portion secured to one prong and the other tothe coil to provide a torsion suspension for the coil to oscillate aboutsaid axis; and a U member having the yoke thereof secured fast to theinner portion of the coil adjacent said end of the core and having armsprojecting into the recess clear of the walls thereof and so near thewalls that the arms prevent radial motion of the coil to a degreesufficient to prevent the coil from coming in contact with the core andconductor.

11. An instrument as claimed in claim 10 said flange 5 being providedwith a radial slot, and said U member being elastic and normally havingthe end portions of the arms substantially perpendicular to the innerWall of the flange.

12. An instrument as claimed in claim 11 there being two U memberssubstantially back-to-back to each other.

UNITED STATES PATENTS Warrington May 7, 1935 FOREIGN PATENTS GreatBritain Jan. 16, 1922 Germany May 13, 1941

